1. Field of the Invention
The invention relates to an ink ejecting device.
2. Description of Related Art
Of non-impact type printing devices which have recently taken the place of conventional impact type printing devices and have greatly propagated in the market, ink-ejecting type printing devices have been known as being operated on the simplest principle and as being effectively used to easily perform multi-gradation and coloration. Of these devices, a drop-on-demand type for ejecting only ink droplets which are used for printing has rapidly propagated because of its excellent ejection efficiency and low running cost.
The drop-on-demand types are representatively known as a Kyser type, as disclosed in U.S. Pat. No. 3,946,398, or as a thermal ejecting type, as disclosed in U.S. Pat. No. 4,723,129. The former, or Kyser type, is difficult to design in a compact size. The latter, the thermal ejecting type requires the ink to have a heat-resistance property because the ink is heated at a high temperature. Accordingly, these devices have significant problems.
A shear mode type printer, as disclosed in U.S. Pat. No. 4,879,568, has been proposed as a new type to simultaneously solve the above disadvantages.
As shown in FIGS. 10A and 10B, the shear mode type of ink ejecting device 600 comprises a bottom wall 601, a ceiling wall 602 and a shear mode actuator wall 603 therebetween. The actuator wall 603 comprises a lower wall 607 which is adhesively attached to the bottom wall 601 and polarized in the direction indicated by an arrow 611. An upper wall 605 is adhesively attached to the ceiling wall 602 and polarized in the direction indicated by an arrow 609. A pair of actuator walls 603 thus formed forms an ink channel 613 therebetween. A space 615 which is narrower than the ink channel 613 is also formed between neighboring pairs of actuator walls 603 in an alternating relationship to the ink channels 613.
A nozzle plate 617, having nozzles 618 formed therein, is fixedly secured to one end of each ink channel 613, and electrodes 619 and 621 are provided as metallized layers on both side surfaces of each actuator wall 603. Each of the electrodes 619,621 is covered by an insulating layer (not shown) to insulate it from the ink. The electrodes 619,621 which face the space 615 are connected to a ground 623, and the electrodes 619,621 which are provided in the ink channel 613 are connected to a silicon chip 625 which forms an actuator driving circuit.
Next, a manufacturing method for the ink ejecting device 600 as described above will be described. First, a piezoelectric ceramic layer, which is polarized in a direction as indicated by an arrow 611, is adhesively attached to the bottom wall 601 and a piezoelectric ceramic layer, which is polarized in a direction as indicated by an arrow 609, is adhesively attached to the ceiling wall 602. The thickness of each piezoelectric ceramic layer is equal to the height of each of the lower walls 607 and the upper walls 605. Subsequently, parallel grooves are formed on the piezoelectric ceramic layers by rotating a diamond cutting disc or the like to form the lower walls 607 and the upper walls 605. Further, the electrodes 619 are formed on the side surfaces of the lower walls 607 by a vacuum-deposition method, and the insulating layer, as described above is provided onto the electrodes 619. Likewise, the electrodes 621 are provided on the side surfaces of the upper walls 605 and the insulating layer is further provided on the electrodes 621.
The vertex portions of the upper walls 605 and the lower walls 607 are adhesively attached to one another to form the ink channels 613 and the spaces 615. Subsequently, the nozzle plate 617, having the nozzles 618 formed therein, is adhesively attached to one end of the ink channels 613 and the spaces 615 so that the nozzles 618 face the ink channels 613. The other end of the ink channels 613 and the spaces 615 is connected to the silicon chip 625 and the ground 623.
A voltage is applied to the electrodes 619,621 of each ink channel 613 from the silicon chip 625, whereby each actuator wall 603 suffers a piezoelectric shear mode deflection in such a direction that the volume of each ink channel 613 increases. The voltage application is stopped after a predetermined time elapses, and the volume of each ink channel 613 is restored from a volume-increased state to a natural state, so that the ink in the ink channels 613 is pressurized and an ink droplet is ejected from the nozzles 618.
However, in the ink ejecting device 600 constructed as described above, the electrodes 619,621 facing the spaces 615 are connected to the ground 623 and the electrodes 619,621 provided in the ink channels 613 are connected to the silicon chip 625 forming the actuator driving circuit so that the voltage is applied to the electrodes 619,621 in each ink channel 613 to eject the ink. Therefore, the electrodes 619,621 in the ink channels 613 must be coated with the insulating layer to be insulated from the ink. If no insulating layer is provided, short-circuiting would occur for the highly conductive ink. Further, even if conductivity of the ink is not so high, the electrodes 619,621 are deteriorated due to electrical or chemical corrosion thereof and thus deflection of the actuator wall 603 is not sufficiently performed so that printing quality is lowered. Accordingly, the insulating layer must be provided to insulate the ink and the electrodes 619,621 from each other and equipment and a process for forming the insulating layer are required. As a result, there occurs a problem that productivity is lowered and cost is increased.
In U.S. Pat. No. 4,879,568 disclosing the ink ejecting device 600, ink is provided only to the ink channels 613. No ink is provided to the spaces 615. However, the structure and method for supplying the ink to this multi-channel ink ejecting device are not disclosed. If it is considered that through holes intercommunicating with the ink channels 613 are provided at the bottom wall 601 or the ceiling wall 602 in correspondence with the respective ink channels 613 to supply the ink into the ink channels 613 while preventing the supply of ink into the spaces 615, it is difficult to form the through holes because of the small size and the yield is low. In addition, the processing or assembly work requires a long time and is unsuitable for mass production.
There has been recently proposed another ink ejecting device as disclosed in U.S. Pat. No. 5,016,028, which can perform higher integration and miniaturization by using a shear mode (thickness shear mode) in deflection modes of piezoelectric material for the occurrence of pressure. The construction of this ink ejecting device will be hereunder described with reference to the accompanying drawings.
As shown in FIG. 11, the ink ejecting device 1 comprises a piezoelectric ceramic plate 2, a cover plate 3, a nozzle plate 31 and a base plate 41.
The piezoelectric ceramic plate 2 is formed of ceramic material of lead zirconate titanate (PZT) having ferroelectricity. The piezoelectric ceramic plate 2 is polarized in the direction indicated by arrow 5. It is then subjected to cutting using a rotating diamond blade 30 to form grooves 28 therein as shown in FIG. 12. During the cutting, the cutting direction of the diamond blade 30 is varied from a direction 30A through a direction 30B to 30C, thereby forming a groove 28 comprising a channel groove portion 17, an arc-shaped groove 19 and a shallow groove portion 16.
The channel groove portion 17 is formed by cutting in the direction 30A by the diamond blade 30. Then the cutting direction is varied from the direction 30A to the direction 30B to change the depth of the cutting work. At this time, the arc-shaped groove portion 19, which is a curved surface having the same curvature as the diamond blade 30, is formed. Subsequently, the cutting direction is varied from the direction 30B to the direction 30C to form the shallow groove portion 16.
As shown in FIG. 11, plural grooves 28 are formed on the piezoelectric ceramic plate 2 which has been subjected to cutting as described above. The grooves 28 have the same depth and are arranged in parallel to one another. The shallow groove portion 16 is formed in the neighborhood of one end surface 15 of the piezoelectric ceramic plate 2. The dimensions of the channel groove portion 17 and the shallow groove portion 16 is determined by the thickness and the cutting depth of the diamond cutter blade 30. The pitch and the number of the grooves 28 is determined by controlling the feeding pitch of a working table and the frequency of groove cutting in the process of forming the grooves 28. The curvature of the curved surface of the arc-shaped groove portion 19 is determined by the diameter of the diamond blade 30. This method is used in semiconductor manufacturing and, needless to say, this method is an effective technique which is usable to perform high integration, etc. required for the ink ejecting device because extremely thin diamond blades of about 0.02 mm thickness are sold in the market. Partition walls 11, which serve as the side surfaces of the grooves 28, are polarized in the direction indicated by the arrow 5.
Metal electrodes 13, 18 and 9 are deposited on the side surfaces of the channel groove portion 17 and the arc-shaped groove portion 19 and the inner surface of the shallow groove portion by a deposition method. As shown in FIG. 13, during the formation of the metal electrodes 13, 18 (FIG. 11) and 9, the piezoelectric ceramic plate 2 is inclined with respect to the vapor emitting direction of a deposition source (not shown). Upon emission of metal vapor from the deposition source, the metal electrodes 13, 18, 9 and 10 are formed at the upper half portion of the side surface of the channel groove portion 17, at a portion from the upper portion of the side surface of the arc-shaped groove portion 19 to a half portion of the side surface of the channel groove portion 17, on the inner surface of the shallow portion 16 and on the upper surface of the partition wall 11 by a shadow effect of the partition walls 11. Subsequently, the piezoelectric ceramic plate 2 is rotated by 180 degrees, whereby the remainder of the metal electrodes 13, 18, 9 and 10 are formed in the same manner as described above. Thereafter, the unnecessary metal electrode 10 which is formed on the upper surface of the partition wall 11 is removed by a lapping method or the like. Through this process, the metal electrode 13 is formed on both side surfaces of the channel groove portion 17 and is electrically connected to the metal electrode formed on the inner surface of the shallow groove portion 16 through the metal electrode 18 formed on the side surface of the arc-shaped groove portion 19.
The cover plate 3 shown in FIG. 11 is formed of a ceramic or a resin material. An ink inlet port 21 and a manifold 22 are formed in the cover plate 3 by grinding or cutting. Thereafter, the surface of the piezoelectric ceramic plate 2 on which the grooves 28 are formed and the surface of the cover plate 3 on which the manifold 22 is formed are adhesively attached to each other with adhesive agent 4 of epoxy group (FIG. 15) or the like. Accordingly, the upper surfaces of the grooves 28 are covered by the cover plate 3, and plural ink channels 12 (FIG. 15) which are arranged at a predetermined interval in a lateral direction are formed in the ink ejecting device 1. Subsequently, ink is filled into all the ink channels 12.
The end surfaces of the piezoelectric ceramic plate 2 and the cover plate 3 are adhesively attached to a nozzle plate 31 in which nozzles 32 are formed so as to confront the respective ink channels. The nozzle plate 31 is formed of plastic such as polyalkylene (for example, ethylene) terephthalate, polyimide, polyether imide, polyether ketone, polyether sulfone, polycarbonate, cellulose acetate or the like.
The base plate 41 is adhesively attached using an adhesive agent of the epoxy group to the surface of the piezoelectric ceramic plate 2 which is opposite to the surface on which the grooves 28 are formed. The base plate 41 is formed with conductive-layer patterns 42 at the positions corresponding to the respective ink channels. The conductive-layer patterns 42 and the metal electrode 9 on the shallow groove portion 16 are connected to each other through a wiring 43 by a well-known wire bonding method or the like.
Next, the structure of the control unit will be described with reference to FIG. 14. FIG. 14 is a block diagram showing the control unit. The conductive-layer patterns 42 formed on the base plate 41 are individually connected to an LSI chip 51. A clock line 52, a data line 53, a voltage line 54 and a ground line 55 are also connected to the LSI chip 51. On the basis of sequential clock pulses supplied from the clock line 52, the LSI chip 51 determines in accordance with data appearing on the data line 53, which nozzle 32 should eject ink droplets. On the basis of this judgment, the LSI chip 51 applies a voltage V from the voltage line 54 to a conductive-layer pattern 42 which is electrically connected to the metal electrode 13 of an ink channel 12 to be driven, and connects the ground line 55 to the conductive-layer patterns 42 which are electrically connected to the metal electrodes 13 of the ink channels 12 other than the ink channel 12 to be driven.
Next, the operation of the ink ejecting device will be described with reference to FIGS. 15 and 16.
In accordance with prescribed data, the LSI chip 51 judges that the ink is ejected from an ink channel 12B of the ink ejecting device 1. On the basis of this judgment, a positive driving voltage V is applied to the metal electrodes 13E and 13F through the conductive-layer pattern 42; the metal electrode 9 and the metal electrode 18 which correspond to the ink channel 12B, and the metal electrodes 13D and 13G are grounded. At this time, a driving electric field, directed as indicated by arrow 14B, occurs in the partition wall 11B and a driving electric field directed as indicated by arrow 14C occurs in the partition wall 11C. In this case, the directions 14B and 14C of the driving electric fields are perpendicular to the polarization direction 5, so that the partition walls 11B and 11C are rapidly deflected toward the inner side of the ink channel 12B due to an effect of the piezoelectric thickness shear mode. Through this deflection, the volume of the ink channel 12B is reduced, and the ink pressure rapidly increases so that a pressure wave occurs, and the ink droplet is ejected from the nozzle 32 (FIG. 11) which intercommunicates with the ink channel 12B.
Further, when the application of the driving voltage V is stopped, the partition walls 11B and 11C are returned to their original position before deflection (see FIG. 15), and the ink pressure in the ink channel 12B is reduced so that the ink is supplied from the ink inlet port 21 (FIG. 11) through the manifold 22 (FIG. 11) into the ink channel 12B.
In the ink ejecting device as described above, the partition walls 11B and 11C at both sides of the ink channel 12B are deflected (deformed) to eject the ink from the ink channel 12B as shown in FIG. 16. However, a portion of the partition wall 11 which corresponds to the side surface of the arc-shaped groove portion 19 is little deflected. Therefore, deflection of a portion of the partition wall 11 which corresponds to the side surface of the channel groove portion 17 contributes to the occurrence of the ink pressure for ink ejecting. That is, the ink filled in the channel groove portion 17 is pressurized, and ink droplet having a predetermined volume is ejected from the nozzle 32 at a prescribed ejecting velocity. Thus, the pressure occurrence which contributes to the ejecting is induced at the channel groove portion 17. The shallow groove portion 16 and the arc-shaped groove portion 19 do not contribute to the pressure occurrence.
Accordingly, there is a problem that the cost of the piezoelectric material for the shallow groove portion 16 and a portion of the arc-shaped groove portion 19 for forming the shallow groove portion 16 for electrical connection with the patterns 42 of the base plate 41, and the material cost of the piezoelectric ceramic plate are high.
Here, electrically, the piezoelectric material constituting the partition walls 11 serves as a kind of capacitor. Therefore, the shallow groove portion 16 and the arc-shape groove portion 19 which substantially do not contribute to the occurrence of pressure are also formed of piezoelectric material. Accordingly, there is a problem that the electrostatic capacity as the capacitor is increased, and thus the efficiency of energy consumed for the pressure occurrence to electrical input energy is low.